#include <iostream>
#include <iomanip>
#include <sys/time.h>
#include <sys/resource.h>

using namespace std;

double getcputime()
{ timeval tim;
  rusage ru;
  getrusage(RUSAGE_SELF, & ru);
  tim = ru.ru_utime;        
  double t = (double) tim.tv_sec + (double) tim.tv_usec / 1000000.0;
  tim = ru.ru_stime;
  t += (double) tim.tv_sec + (double) tim.tv_usec / 1000000.0;
  return t; }

int num_calls = 0;

int num_parties(int members, int size)
{ num_calls += 1;
  if (size == 0)
    return 1;
  else if (size == members)
    return 1;
  else                                              // Consider arbitrarily chosen member X
    return num_parties(members - 1, size - 1) +     //    do we invite him/her/it?
           num_parties(members - 1, size); }        //    or don't we?             no other possibilities

int main(int argc, char * argv[])
{ if (argc != 3)
  { cerr << "usage: " << argv[0] << " members party-size\n";
    exit(1); }
  num_calls = 0;
  int members = atol(argv[1]);
  int size = atol(argv[2]);
  double t1 = getcputime();
  int answer = num_parties(members, size);
  double t2 = getcputime();
  cout << "There are " << answer <<
          " possible different parties of " << size <<
          " from a population of " << members << "\n";
  cout << num_calls << " function calls\n";
  cout << setprecision(6) << t2 - t1 << " seconds\n"; }